This research proposal seeks to delineate the mechanisms of action of luteotropic agents on steroidogenesis in corpus luteum. An in vitro system in which dispersed, homogeneous luteal cells will be examined during the continuous or pulsed supply of substrate and/or regulatory agents will be used. Changes in cell function will be correlated with secretion rates of progesterone and 20alpha-dihydroprogesterone. The following more specific aims are presented: 1. To correlate the luteal cell binding of labeled hCG and PRL with steroidogenesis. 2. To study the rates of gonadotropin-receptor dissociation with consideration for hormone internalization and receptor desensitization. 3. To study the utilization of cholesteryl esters of low density lipoproteins as substrate for steroidogenesis by dispersed luteal cells and mitochondria. 4. To study the mechanism of protein kinase stimulation of luteal mitochondrial steroidogenesis. 5. To define effects on steroidogenesis of potential activators, e.g., estradiol-17beta, PGE2, cholera toxin, etc., during perifusion. 6. To define effects on steroidogenesis of potential inhibitors, e.g., aminoglutethimide, cytocholasin B, cycloheximide, isoxozole, PGF2 alpha, LH binding inhibitor, etc., during perifusion of luteal cells and mitochondria. 7. To use long term perifusion of luteal cells to initiate luteolysis.